Metallic pigment



Patented July '29, 1941 METALLIC PIGMENT Clarence P. Harris, ew York, N.Y., assignor, by mesne assignme ts, to United States Metal Powders,Inc., Baltimore, Md., a corporation 01 Maryland No Drawing. Application-February 19, 1937, Se-

rial No. 126,639. Renewed January 4, 1940 15 Claims. (Cl. 106 -290) Thisinvention relates to the production of metallic pigments in a formconvenient for mixing with the desired vehicle, which effects a moreconvenient covering power of the metal powder,

and eliminates the dusting nuisance of metals in their customarypowdered state, and likewise imparts to the metal flake an increasedleaflngpower, or at least does not cause a diminution in leafing power,as is often the case with products of this type and nature, especiallyupon standing iora considerable period of time.

This application is a continuation in part of my co-pending application,Ser. No. 755,635, filed Dec. 1, 1934, for Production of metallic pigmentpaste.

So called bronze powders consist of minute metallic particles in flakeform, this shape giving the greatest covering and leafing properties.These powder particles vary in size from about 200 to 325 mesh thisbeing the number of meshes per linear inch of sieve through which theywill pass. Such fine powders, especially when composed of comparativelylight metals as aluminum, dust easily into the air, are troublesome tohandle, and diificult to wet.

I have found that a powder of this character may conveniently be madeinto the form of a paste by mixing with it a solvent of the vehicle itis desired to employ, in which condition the dusting property issubstantially eliminated or reduced to a point where it is commerciallynonobjectionable, such paste containing therein a product tending toaugment the. leafing characteristics, the pigment mixture mixing readilywith the vehicle.

Furthermore, the leafing power of the powder in the form of paste isgreatly increased over that exhibited by the dry powder. The leafing orcovering power of the pigment in paste condition is increased in thepresent invention in at' least two ways, not only because the metallicparticles are completely separated or substanporation with thesolventportion or certain organic sublimable solids and/ or a colloidal sol.

This not only makes it easier to obtain a uniform distribution of themetallic particles throughout the viscous vehicle of the paint, lacquer,varnish, enamel, or other type of protective coating, but by increasingthe physical stability of the mixture as a whole, normal coalescence ofindividual particles is. substantially entirely prevented, and theindividual particles remain as such, free movement upon dilution, withno observable agglomeration or coalescence, heretofore observed in theart. A more effective use of the metallic particles, or pigment may thusbe obtained, on account of an increased opacity and covering power perunit weight of metallic flake.

Metallic powders, especially of the aluminum metal type, in contact withorganic liquids of the class normally employed in protective coatingcompositions, usually accelerate decomposition of such liquids,sometimes with the liberation of acids or products which act as acidsand which appear to attack the thin metal particles, causing them toadhere or coalesce. Metallic pigments therefore are not mixed with theirvehicles until immediately before use in the majority of instances, inorder to minimize such difllculties primarily due to decomposition.

Whilst this decomposition is more marked with the entire vehicle, theintensity and speed of decomposition depending in a measure upon thenature of the vehicle and the relative purity and compatibility of thecomponents constituting the same, decomposition also occurs with thesolvent alone, especially with such organic liquids as commercialpetroleum hydrocarbon fractions, usually highly complex and of widelyvarying chemical composition, and containing relatively small amounts ofvarious impurities depending primarily upon the nature of the originalpetroleum product operated upon and the precision of purification towhich it has been subjected. Such hydrocarbon fractions are frequentlyused as diluents of vehicles for metallic pigments, either alone, orwhere cellulose .esters are employed as in the lacquer type ofprotective coatings, in conjunction with esters, ketones, alcohols andother bodies having a solvent, colloiding, or plasticizing action uponthe cellulose compound.

This tendency to decomposition is especially noticeable when thesehydrocarbon mixtures contain small and varying amounts of impuritiessuch as sulfur and/or nitrogenous compounds.

55 The decomposition of the solvent has a deleterious effect upon thebrilliancy and the leaflng quality of the metallic powder, especiallywhen that powder is aluminum.

It therefore is a further object of the present invention to stabilizepastes or mixtures of metallic powders, especially when the metallicparticles are in flake or leai' form, when said powders are incorporatedwith solvents of the type or nature of those used in protectivecoatings, as of the classes hereinbefore indicated, and in sostabilizing the same, to permit the augmentation of leaflngcharacteristics which usually proceeds upon storage and ageing ofpowders of this nature when properly prepared.

In accordance with the present invention, stabilization is attained, andpreserved, thus allowing normal augmentation of. leaflng characteristicsto develop and increase, by adding to the mixtures of metallic powderswith organic solvents or solvent combinations, certain neutralhydrocarbon, alcoholic or ketonic bodies of relatively high boilingpoint, readily sublimable at ordinary temperatures, soluble in thesolvents normally used in protective coatings of this nature, ofrelatively high stability yet of comparatively low volatility, examplesbeing naphthalene, and other substituted naphthalenes and naphthalenicbodies, natural and synthetic camphors and camphoraceous bodies andcamphor substitutes, only when they fulfill the conditions and exhibitthe properties as heretofore enumerated, and which when added to theliquid portion of the paste or colloidal sols, tend to preserve andstabilize the paste.

In each instance, however, the stability-inducing body or bodiespromoting leaflng characteristics are compatible with the vehiclesolvent, and in those protective coatings and compositions of lacquertype, wherein cellulose esters'are employed as a portion or all of thenon-metallic non-evaporable solids portion, the leaflngenhancing bodiesherein disclosed, possess the additional value that often they aredirect or ancillary solvents for the cellulose compound, thus admittingof a greater amount of cellulose ester nonsolvent portion in thecomposition, as the petroleum hydrocarbon fractions heretoforementioned.

Simple mixtures of metallic powder with an organic liquid of the typeused in protective coatings, are likely to separate into layers ofgreater and lesser pigment concentration, so that the paste will lackhomogeneity. This is true of pastes containing as much as 65% metallicpigment.

Tb prevent or delay such a separation, thickening or viscosity-inducingagents which apparently form true colloidal sols with the liquids areemployed. Such agents not only maintain the initial homogeneity of thepaste, but by virtue of their presence, in the quantity ratios as hereindisclosed, prevent or slow up decomposition to the point wherein it isunnoticeable or unobjectionable, and thereby permit the augmentation ofleafing characteristics to proceed without inhibition, primarily bymaintaining in the composition upon standing, a'stabilizing influenceor'condition, optimum for the promotion of leaflng and the conservationof brilliancy.

As a specific example exemplifying my invention, I may take 32.5 gramspolished aluminum powder in leaf form, mix the same mechanically with 19grams petroleum hydrocarbon fraction of suitable boiling range and ofrelatively high purity from components not hydrocarbons, and in which isincorporated 0.2 to 0.8 gram camphor or analogous aromatic ketone. Theaddition of 10% camphoras a specific example-to a pctroleum fractionboiling at about 160 to 180 deg. 0. increases the leaiing power of thepaste made therefrom from 10% to 20% above that made in the absence ofcamphor, or camphor equivalent.

For example, I prepared a liquid as follows: 90 gms. petroleum fractionof boiling range approximately as above stated, and 10 gms. gum camphorwas heated together until the camphor was dissolved, although it is notnecessary to heat camphor with such a petroleum fraction in order toinduce solution. One gm. of aluminum stearate and 3gms. commercialhighly purifled stearic acid, presumably containing a relatively smallamount of stearime) were then added and the mixture heated untilcomplete solution was obtained. After cooling to approximately roomtemperature, pastes made by mixing gms. of liquid with 65 gms. aluminumpowder in flake form showed 20% greater leaflng power than that obtainedin the same manner but without the addition of the camphor.

In a formula representative of my invention employing a metal with asol, I select an aluminum powder conforming to the physical and chemicalspecifications heretofore indicated, and prepare a colloidal sol asfollows:

Take 200 parts of a petroleum or coal tar distillate within the boilingrange of about 155 to 175 C. This hydrocarbon fraction may be composedentirely of aliphatic hydrocarbons or a mixture of aliphatic andaromatic hydrocarbons.

I have found a mixture of decanes to dodecanes,

combined with the xylenes to produce especially advantageous andunobvious results in connection with high molecular acids and theirmetallic salts in this connection.

To the mixture of hydrocarbons is added 0.6 gram metallic stearate asaluminum stearate, the mixture beingintroduced into a flask of suitablesize provided with reflux condenser. The mixture is heated to incipientebullition for about a half hour, cooled to around 80 0., and there isthen added 6 to 6.5 parts commercial stearlc acid or equivalent. Whencompletely dissolved, cool to room temperature.

The sol is now in normally suitable condition for immediate use, or itcan be further homogenized by passing the same through a colloid mill,as one with a tight gap about one onethousandth inch (0.001") for abouttwo minutes, when it may be stored for use.

sisting in the preservation of the metal particle paste for prolongedperiods.

An excellent composition has been obtained by me by incorporating 66.6parts metal particle with 33.4 parts of the composition above, stirringgently in order to avoid abrasion or attrition, which has a tendency todiminish the leailng propensity. It is preferable to allow the materialto stand for a time before use, say about 24 I my invention.

hours, when a definite equilibrium appears to be reached.

The above forms an excellent paste for decora-' tive work and protectivecoatings. It usually has a leafing property of the order of 60% orhigher, together with good physical and chemical stability.

Or, I may take 67 parts of aluminum particle as in the foregoingexample, and add thereto the following: A petroleum or coal tardistillate or admixture thereof, of boiling range in the vicinity of 175G. Take 28.4 parts of this purified hydrocarbon mixture and dissolvetherein 0.1 part anhydrous aluminum stearate, 1% stearic acid (hotpressed) and 3.5 parts camphor, camphoraceous body or camphorsubstitute, provided the same is substantially all soluble in thehydrocarbon portion. This paste will have an initial leafing andmirroring capacity of from 10% to in excess of a paste asmade by theformula outlined in the preceding example. This increased leafing willpersist for an indefinite period, especially if the paste is stored in ahermetically sealed container. The augmented leafing property slowlydiminishes after the container contents has been exposed to the air, butthe physical and chemical stability ofthe paste is excellent.

In another series of examples, using the quantities of components aboveenumerated, but in which the amount of aluminum stearate and stearicacid was successively reduced in quantity until they were entirelyabsent from the formula, still satisfactory promotion of leafing ormirroring characteristics was obtained.

I have described herein what I believe to be Y typical examplesandpreferred embodiments of I do not wish, however, to be confined tothe embodiments described, or the quantities of components stated, butwhat I desire to cover by Letters Patent is set forth in the appendedclaims. 1

I claim: a

1. A metallic pigment paste formed by mixing a metallic powder with acolloidal sol with camphor which causes the paste to have a greaterleafing power than the same weight of dry powder.

'2. A metallic pigment paste formed by mixing a metallic powder with acolloidal sol with a camphor body which causes the paste to have agreater leafing power than the same weight of dry powder.

3. A metallic pigment paste formed by mixing metallic aluminum particlesin leaf form with a petroleum fraction of hydrocarbons of high purityhaving a boiling point range of 160 to 200 C. containing dissolvedtherein a readily sublimable solid, neutral, volatile aromatic ketone,in proportion to promote leafing of the pigment portion. 4. Method forpromoting the leafing of a. pigment consisting of a plurality ofaluminum par-- ticles in flake form, comprising incorporating saidpigment into a high flash point naphtha, in which has been dissolved aproportion of naphthalene.

5. An improved method for augmenting the leafing characteristics of apigment mixture comprising particles of aluminum in flake form,consisting of dissolving a neutral, readily sublimable organic solid ofthe group consisting of aromatic ketones, naphthalene and substitutednaphthalenes in a highly purified mixture of aliphatic hydrocarbons ofsuitable boiling range, and incorporating the same with the metallicparticle proportion to the consistency and metal content required,substantially as herein set forth.

6. An improved method for augmenting the leafing characteristics of apigment mixture comprising particles of aluminum in flake form.consisting of dissolving a neutral, readily sublimable organic solid ofthe group consisting of neutral hydrocarbon bodies and aromatic ketonesin a highly purified mixture of aromatic hydrocarbons of suitableboiling range, and incorporating the same with the metallic particles inproportion to the consistency and metal content required, substantiallyas herein set forth.

7. A metallic pigment paste formed by mixing a metallic powder with astable colloidal sol containing in addition a neutral hydrocarbon bodysolid at ordinary temperature but which readily sublimes at suchtemperature and causes an increase in the leafing power of the paste.

8. A metallic pigment paste whichpromotes leafing of a pigment composedof finely divided aluminum particles in flake form intimately mixed witha stable colloidal sol containing in addition a readily sublimablesolid, volatile aromatic hydrocarbon dissolved in a paraffln hydrocarbonfraction of relatively high purity.

9. A metallic pigment paste composed of finely divided particles ofaluminum particles in flake form intimately mixed with a stablecolloidal sol containing a proportion of camphor, aluminum stearate andstearic acid dissolved in a petroleum fraction having a boiling pointrange of to 200 C. in such amount and under such conditions as topromote the leafing of the pigment.

10. A metallic pigment paste formed by mixing a metallic powder with astable colloidal sol and formed of a metallic soap dispersed in a liquidphase of the'paste and containing in addition an organic compound solidat ordinary temperature but which sublimes at such temperature and whichcauses an increase in the leafing power of the paste, said organiccompound comprising camphor.

11. A metallic pigment paste composed of me-- tallic particles in leafform mixed with a petroleum fraction of hydrocarbon of high purityhaving dissolved therein a readily sublimable, solid, neutral, volatilehydrocarbon body in amount sufficient to promote the leafing of themetal particles.

12. A metallic pigment paste composed of finely divided metallicparticles mixed with a solution containing a colloidal sol consisting ofhigh flash point naphtha, a metallic stearate and naphthalene in amountsufiicient to promote the leafing power of the metal particles.

13. A metal pigment composition of improved leafing characteristicscomprising an intimate mixture of metallic powder, a volatilehydrocarbon liquid, a higher fatty acid as leafing agent, and a normallysolid readily sublimable aromatic stabilizing agent selected from thegroup consisting of camphor, naphthalene, and camphoraceous andnaphthalenic bodies.

14. A stabilized metal pigment paste having improved leafing powercomprising metal flakes. stearic acid, a substituted naphthalene, and athinner.

15. A stabilized metal pigment paste having-

